Trace metals can provide a new window to past climate

Posted 14 November 2011

Stalagmites can be important archives of previous climatic conditions.

A recent study led by Connected Waters Initiative researcher Adam Hartland has shown how analysis of the trace metals in cave deposits can provide important clues about climatic conditions in the past.

Deposits found in caves, such as stalagmites, are typically formed by groundwater originating at the surface - a process influenced by climatic conditions. Because of this relationship, researchers focus on these deposits in order to reveal information about past climate.

The new findings show the extent to which the abundance of certain trace metals in groundwater entering a cave is determined by interactions with colloidal organic particles - particles with dimensions between 1 billionth of a metre and 1 millionth of a metre.

By demonstrating this association between colloidal organic matter and trace metals in the cave waters, the study has concluded it may be possible to derive information about the movement of organic materials between soils and groundwater by measuring the trace metal contents of stalagmites formed from them.

The organic colloids and trace metals, which occur naturally in soil at the surface, are transported into cave environments as water percolates through the soil into cave systems below.

Since this process is mediated largely by climate, the abundance of trace metals in stalagmites can therefore be used to infer climatic conditions (e.g. dry/wet episodes) prevailing during the period when the stalagmites were formed.

This is significant, because until now, researchers have generally treated the organic and inorganic constituents of cave waters in isolation, and interactions between these components had not previously been identified in waters that form stalagmites in caves.

Trace metals may be chemically bound in "complexes" with organics that can act to stabilise them in solution and enable their migration over long distances in groundwater systems. This process is known as "colloid-facilitated transport".

The study focused on stalagmite-forming waters from a very high pH, or "hyperalkaline" cave system in which the process of metal-binding and transport is probably enhanced.

It found binding of metals such as copper, nickel and cobalt, occurred with both truly dissolved and colloidal organic species below 0.1 millionths of a metre in size. Organic colloids have very large specific surface areas (area/volume) to which comparatively large amounts of metals can be bound.

Because they are typically present in natural waters in much greater numbers than particulates, organic colloids can therefore play a significant role in the transport of trace elements from the surface into caves.

Further work is needed to understand this process in less-alkaline waters found in the majority of caves. Because it is likely this process would be fairly ubiquitous in the karst (limestone) systems where caves occur, the findings of this study may have broad relevance for the study of cave deposits such as stalagmites to obtain information about past climates and their hydrology.

The paper by appears in the 75 volume of the geochemistry journal Geochimica et Cosmochimica Acta.

Links

Latest news

Floating though the dolines

Floating though the dolines

24 July 2020

Are you a fan of ABC's Conversations with Richard Fidler? Well, you might want to take a listen to this episode of the program with subterranean ecologist Stefan Eberhard.  

Read more…

New questions over Shenhua water modelling

New questions over Shenhua water modelling

24 July 2020

Take a listen to ABC Radio National Breakfast's segment on the controversial $1.5 billion Shenhua thermal coal mine on the New South Wales Liverpool Plains. Research undertaken by UNSW's leading groundwater expert Professor Ian Acworth indicates that the company's water modelling is flawed.

Read more…

Ban on toxic mercury looms in sugar cane farming, but Australia still has a way to go

Ban on toxic mercury looms in sugar cane farming, but Australia still has a way to go

18 July 2020

CWI's Professors Cameron Holley and Darren Sinclair and Australian National University's Professor Simon Haberle and Larissa Schneider recently contributed to The Conversation, discussing federal authorities announcement of "an upcoming ban on mercury-containing pesticide in Australia", highlighting Australia is "one of the last countries in the world to do so, despite overwhelming evidence over more than 60 years that mercury use as fungicide in agriculture is dangerous." 

Read more…

Ancient water to drain from farmland without ongoing joint management

Ancient water to drain from farmland without ongoing joint management

1 July 2020

The management of withdrawals of ground water in the Central West remains an area of hotly-contested debate. Associate Professor of Hydrogeology Bryce Kelly has spent over a decade studying groundwater in the Central West, and has credited groundwater with “saving rural communities from collapse”, but its potential for future drought-proofing depends on how successfully it’s managed. He says current withdrawals “will only be sustainable if the Narromine region gets flooded frequently enough to balance the volume of groundwater extracted."

Read more…

GWI Global Water Matters Podcast

21 June 2020

The UNSW-GWI Global Water Matters Podcast was launched in 2020 to share interesting and important water-related developments and insights from global experts across the broad spectrum of water-related disciplines. Born from the demand to continue the Water Issues Commentary seminar series under the constraints of social distancing, new episodes are released monthly.

Read more…